Ultrasonic standing wave spraying arangement

ABSTRACT

The invention relates to an ultrasonic standing-wave atomizer arrangement  10, 40, 50, 60, 70, 80  for producing a paint spray mist for painting a workpiece, with a sonotrode  12, 48  and with a component  14, 46  arranged lying opposite the sonotrode  12, 48.  A standing ultrasonic field is formed in the intermediate space between the sonotrode  12, 48  and the component  14  in the case of operation. A paint-feeding device  29,  by means of which paint can be fed into the vicinity of a maximum of the sound particle velocity of the ultrasonic field, is provided. The paint-feeding device has in the region of the standing ultrasonic field at least two pieces of pipe  30, 31, 32; 42, 43, 44  for discharging paint, at least two of the pieces of pipe  30, 31, 32; 42, 43, 44  being arranged in the region of a selected maximum of the sound particle velocity of the standing ultrasonic field.

The invention relates to an ultrasonic standing-wave atomizerarrangement for producing a paint spray mist for painting a workpiece,with a sonotrode, with a component arranged lying opposite thesonotrode, a standing ultrasonic field being formed in the intermediatespace between the sonotrode and the component in the case of operation,and with a paint-feeding device, by means of which paint can be fed intothe vicinity of a maximum of the sound particle velocity of theultrasonic field.

For painting workpieces, in particular in mass painting as frequentlyencountered in the automobile industry, at present the generally knownhigh-rotation atomizers are preferably used. In the case ofhigh-rotation atomization, the paint is passed through the interior of ametal bell and in this way reaches the front side of the latter, facingthe workpiece. The metal bell is usually driven by a compressed-airturbine and rotates at up to 80 000 revolutions per minute. Thecentrifugal forces acting in this case then cause the paint to reach thefront-side edge of the bell, to break away there in fine droplets. Thisachieves the effect that the droplet size of the paint spray mistrequired for adequate quality of a coat of paint lies in the range from10 μm to 60 μm.

Considerations of the fundamentals which have become generally knownindicate that, in principle, paint can also be atomized by means ofultrasonic standing-wave atomization. Following these considerations ofthe principles concerned, however, average droplet sizes duringatomization of between 100 μm. and 200 μm. have been measured, with someinstances of still larger drops occurring. However, large drops of thiskind adversely influence the quality of the coat of paint in such a wayas to make use in painting technology unattractive.

It has been proposed how an ultrasonic standing-wave atomizerarrangement for producing a paint spray mist for painting a workpiececan be designed to achieve smaller droplet sizes. For example, specificdesigns of the sonotrode and of the component, shut-off elements ormulti-piece rings, which improve the quality of the paint spray mistproduced and consequently allow comparatively small droplet sizes to beachieved, have become known. A disadvantage is that only comparativelylow delivery rates of paint can be atomized by the arrangement that hasbecome known.

On the basis of this prior art, it is the object of the invention toprovide an ultrasonic standing-wave atomizer arrangement for producing apaint spray mist with which it is possible to increase the atomizedamount of paint, that is the rate of paint, and at the same time tomaintain a selected range of droplet sizes occurring.

This object is achieved by the ultrasonic standing-wave atomizerarrangement according to the invention for producing a paint spray mistfor painting a workpiece with the features specifed in Claim 1.

The ultrasonic standing-wave atomizer arrangement according to theinvention, of the type stated at the beginning, accordingly has apaint-feeding device, which has in the region of the standing ultrasonicfield at least two pieces of pipe for discharging paint. Moreover, atleast two of the pieces of pipe are arranged in the region of a selectedmaximum of the sound particle velocity of the standing ultrasonic field.According to the invention, it is therefore provided that a selectedmaximum of the sound particle velocity of a standing ultrasonic wave isused for the purpose of atomizing a comparatively large amount of paintinto paint droplets. This is so because it has been found that, inparticular in the case of ultrasonic standing-wave atomizer arrangementsof a simple construction, a selected maximum of the sound particlevelocity is often particularly well formed in the standing ultrasonicfield, for example in the case of standing ultrasonic fields with anuneven number of sound particle velocity antinodes, the middle soundparticle velocity antinode. That is to say that this maximum isparticularly stable, with a comparatively high sound particle velocity.These particularly good atomizing properties of the selected maximum areused according to the invention for increasing the amount of paint to beatomized or the flow of paint through the paint-feeding device and it isprovided that at least two pieces of pipe for discharging paint arearranged in the region of the selected maximum. Consequently, the amountof paint to be atomized can be increased in an advantageous way. Anadvantageous design of the ultrasonic standing-wave atomizer arrangementaccording to the invention is achieved if the component is a furthersonotrode. In this way, the atomizing capability of the standingultrasonic field can be increased. Moreover, a more stable ultrasonicfield can be formed in this way.

A further advantageous refinement of the subject-matter of the inventionprovides that the distance between the pieces of pipe in the region ofthe selected maximum is so great that sheets of paint that are separatefrom one another are formed for each piece of pipe. For technicalvibration-related reasons, a sheet of paint is respectively formed inany case on the pieces of pipe, extending from the paint outlet point.If the distance between the pieces of pipe has been chosen to be greatenough that the sheets of paint can form separately from one anotherwithout influencing one another, the region in which droplets ofdifferent sheets of paint collide and in this way can recombine to formlarger droplets is avoided in any case. The quality of the paint spraymist is improved with the proposed arrangement.

It is particularly advantageous if the paint outlet openings of the atleast two pieces of pipe in the region of the selected maximum of thesound particle velocity of a standing ultrasonic wave are arranged on astraight line, and if the straight line is perpendicular to an imaginarycentre line which passes through the centroids of the opposing soundfaces of the sonotrode and of the component. In the case of anarrangement of this type, the distance between the paint outlet pointson the pieces of pipe and the sonotrode or the component arerespectively of approximately the same size. A particularly advantageousposition, seen in the X direction, is achieved in the region of themaximum of the sound particle velocity.

The advantage mentioned above may also be achieved if three pieces ofpipe are arranged in the region of a selected maximum of the soundparticle velocity of a standing ultrasonic wave, and if these pieces ofpipe or their paint outlet openings are arranged in a triangle. Anarrangement in an equilateral triangle is particularly favourable. It isa further improvement if that area which is determined by the triangleis perpendicular to an imaginary centre line which passes through thecentroids of the opposing sound faces of the sonotrode and of thecomponent. In this case, too, the effect is in turn achieved that, seenin the X direction, the paint outlet openings are situated in the regionof the maximum of the sound particle velocity.

It has also been found that the atomizing operation or the atomizingrate can be improved by choosing the specific maximum such that it iscloser to the sonotrode than to the component. There is then thepossibility of the so-called capillary wave turbulence effect, that isto say the effect which keeps the paint droplets away from the sonotrodeas a result of the vibrations of the latter and in this way assists theatomization process.

Further advantageous refinements of the subject-matter of the inventioncan be taken from the dependent claims.

The invention, its advantages and further improvements of the inventionare explained and described in more detail on the basis of the exampleembodiments specified in the drawings, in which:

FIG. 1 shows a first ultrasonic standing-wave atomizer arrangement,

FIG. 2 shows a second ultrasonic standing-wave atomizer arrangement,

FIG. 3 shows a third ultrasonic standing-wave atomizer arrangement,

FIG. 4 shows a fourth ultrasonic standing-wave atomizer arrangement,

FIG. 5 shows a fifth ultrasonic standing-wave atomizer arrangement,

FIG. 6 shows a sixth ultrasonic standing-wave atomizer arrangement.

FIG. 1 shows a first ultrasonic standing-wave atomizer arrangement 10according to the invention in an isometric representation. Thecoordinates are indicated by the directional arrows for the X, Y and Zdirections in a system of Cartesian coordinates. Moreover, therepresentation is intended to be only of a schematic character, with theresult that the actual relative sizes cannot be taken from this figure.

A first sonotrode 12 is arranged lying opposite a first reflection body14. In this figure, the sonotrode 12 is schematically represented by acylindrical basic body 16 and a sound body 18, which protrudes from theend face of the cylindrical basic body 16 facing towards the reflectionbody 14. The sound body 18 and the basic body 16 have an approximatelycylindrical form. The opposing end faces of the sound body 18 and of thefirst reflection body 14 are to be referred to as the first sound face20 for the end face on the sound body 18 and as the second sound face 22for the end face on the reflection body 14. The first sound face 20 andthe second sound face 22 are concavely formed, that is to say their formcorresponds approximately to a portion of the surface of an imaginaryhollow sphere. To illustrate this form, a first dotted line 24 and asecond dotted line 26 have been drawn on the first sound face 20. Thepoint of intersection between the first line 24 and the second line 26lies exactly centrally on the first sound face 20. Lines correspondingto the first line 24 and the second line 26 are also shown on the secondsound face 22, without however being provided more specifically withreference numerals. Also shown through the point of intersection of thefirst line 24 with the second line 26 and also the corresponding linesof the second sound face 22 is a centre axis 28, which runs exactly inthe direction of the X coordinate.

Shown in the intermediate space between the first sound face 20 and thesecond sound face 22 is a first piece of pipe 30, a second piece of pipe31 and a third piece of pipe 32, the free ends of which are arrangedexactly midway between the sound faces 20, 22. That is to say that thepieces of pipe 30, 31, 32 are arranged next to one another, the freeends all lying in one plane, which is defined by the centre axis 28 andthe second line 26. Moreover, all the free ends can be joined by animaginary straight line. The longitudinal axes of the pieces of pipe 30,31, 32 are arranged parallel to the Y direction and are connected bytheir ends remote from the ends to a paint-feeding device 29 (notrepresented any more specifically in this figure), which provides therequired amount of paint to be atomized by the first ultrasonicstanding-wave atomizer arrangement 10. However, the idea of theinvention also includes the option of each of the pieces of pipe 30, 31,32 being respectively connected to a separate paint-feeding device 29.This is in any event also to be intended by the paint-feeding device 29described here.

The other end of the pieces of pipe 30, 31, 32 therefore ends as it werein “free space”, without which the connection to the paint-feedingdevice 29 would be represented.

To allow better illustration of the processes taking place in thestanding ultrasonic field between the first sound face 20 and the secondsound face 22, the profiles of five sound particle velocity antinodes ofthe standing ultrasonic wave have been shown in the intermediate space,the profiles being represented about the centre axis 28, to be precisein the plane defined by the X direction and Y direction. In the examplechosen, a first distance 34 between the first sound face 20 and thepieces of pipe 30, 31, 32 and a second distance 36 between the pieces ofpipe 30, 31, 32 and the second sound face 22 are of the same size. It isconsequently clear that the free ends concerned of the pieces of pipe30, 31, 32 are also situated at only one maximum of the sound particlevelocity, that is to say in the middle one of the five sound particlevelocity antinodes. In the design of the first ultrasonic standing-waveatomizer arrangement 10 that has been chosen for this arrangement, afirst distance 34 and a second distance 36 of 17 mm are obtained for anultrasonic frequency of 24 kHz and five sound particle velocityantinodes. That is to say that adequate space is available for cleaningor directing air which is possibly used for assisting the atomizationprocess or for directing the particles of paint. With such anarrangement of three pieces of pipe 30, 31, 32 in only one soundparticle velocity antinode, that is in the region of a maximum of soundparticle velocity, the advantageous effect is therefore achieved thatparticularly high rates of paint, in particular rates of paint of morethan 200 ml/min, are readily achievable. Moreover, it is ensured thatthe distribution of the diameters of the drops of atomized paint remainin an acceptable range. The atomizing operation is only symbolicallyrepresented in this figure at the respective free ends of the pieces ofpipe 30, 31, 32, in that many small paint particles are indicated aroundan exaggerated atomization bubble.

FIG. 2 shows a second ultrasonic standing-wave atomizer arrangement 40,which is intended to have substantially the same components as the firstultrasonic standing-wave atomizer arrangement 10, for which reason thesame reference numerals have been chosen for equivalent components. Amajor difference between the first ultrasonic standing-wave atomizerarrangement 10 and the second ultrasonic standing-wave atomizerarrangement 40 is that, unlike in the arrangement shown in FIG. 1, thearrangement of the pieces of pipe 30, 31, 32 no longer takes placemidway between the sound body 18 and the first reflection body, butcloser to the sound body 18. The arrangement of the pieces of pipe 30,31, 32 is chosen such that their paint outlet openings in turn come tolie at a selected maximum of the sound particle velocity of the standingultrasonic wave, to be precise at the second maximum shown, as seen fromthe sound body 18. That is to say therefore that a third distance 38between the sound body 18 and the pieces of pipe 30, 31, 32 is less thana fourth distance 39, which is determined as the distance between thepieces of pipe 30, 31, 32 and the first reflection body 14. In the caseof the arrangement shown here, it proves to be an advantage that thepieces of pipe 30, 31, 32 lie closer to the first sonotrode 12. This isso because it has been found that the vibrations of the sound body 18 ofthe first sonotrode 12 stop the atomized paint droplets comparativelywell from adhering to the sonotrode due to the vibration of the soundbody 18 itself. Or to put it another way, the vibrations of the soundbody 18 keep the paint droplets away from it.

In addition, the representation of the pieces of pipe 30, 31, 32 and theatomization bubbles indicated with the atomized paint particles showthat the distance between the pieces of pipe 30, 31, 32 is chosen suchthat atomizing regions that respectively operate independently of oneanother form at the free ends of the pieces of pipe 30, 31, 32, that isto say that sheets of paint that are separate from one another areformed for each piece of pipe 30, 31, 32. This has the advantage thatthe regions in which the discharged paint is atomized into particles donot disturb one another. Consequently, the atomizing operation isimproved and a comparatively high atomizing rate is achieved.

FIG. 3 shows a further advantageous possibility for refining thesubject-matter of the invention, with a third ultrasonic standing-waveatomizer arrangement 50, which is of a substantially similarconstruction to that of the first ultrasonic standing-wave atomizerarrangement 10. To make it easier to compare between the componentsused, the same reference numerals have therefore been used in turn forcomparable components.

A major difference between the arrangement in this figure and that inFIG. 1 is that in this figure a fourth piece of pipe 42, a fifth pieceof pipe 43 and a sixth piece of pipe 44 are arranged exactly midwaybetween the sound body 18 and the first reflection body 14. Although thecorresponding paint outlet openings of the pieces of pipe 412, 43, 44are accordingly arranged in turn in the region of the central maximum ofsound particle velocity, the paint outlet openings no longer lie in theplane defined by the X and Z directions, but instead the middle, fifthpiece of pipe 43 lies in the positive Y direction, above the planedefined by the X and Z directions, while the fourth piece of pipe 42 andthe sixth piece of pipe 44 lie underneath the plane defined by the X andZ directions. However, all three paint outlet openings still lietogether in a plane parallel to a plane defined by the Y and Zdirections. The three paint outlet openings therefore form as it were animaginary triangle which is situated in a plane parallel to the planedefined by the Y and Z directions. This design has the advantage thatthe distance between the paint outlet openings can be further increasedwithout leaving the chosen, one maximum of the sound particle velocity.In this way, the atomization can be further improved and at the sametime the rate of paint can also be increased.

FIG. 4 shows a fourth ultrasonic standing-wave atomizer arrangement 60with a second reflection body 46, which is arranged lying opposite asecond sonotrode 48. Three first small paint pipes 52 are in turnarranged midway between the second reflection body 46 and the secondsonotrode 48. In a way similar to that already shown in FIG. 1, thepaint outlet openings of the first small paint pipes are aligned alongan imaginary line in the Z direction. A special feature of thearrangement shown is that a second sound body 54 on the second sonotrode48 and also the second reflection body 46 have approximately a cuboidalform, the opposing sound faces of the second sound body 54 and of thesecond reflection body 46, that is to say the third sound face 56 on thesecond sound body 54 and the fourth sound face 48 on the secondreflection body 46, having a form which corresponds to a portion of thegenerated surface of a cylindrical body.

In this case, it proves to be an advantage if the imaginary centre axisof the cylindrical body runs parallel to that line 62 which runs throughthe paint outlet openings of the first small paint pipes 52. Theprojections 64 of the centre axis of the imaginary cylinder on the thirdsound face 56 and on the fourth sound face 58 are drawn as dotted lines.Such an arrangement achieves the effect that the maximum of the soundparticle velocity in the stationary ultrasonic field is as wide aspossible, that is to say it has an extent which is as great as possiblein the direction of the line 62, which coincides here with the Zdirection.

A fifth ultrasonic standing-wave atomizer arrangement 70 is shown inFIG. 5. In this case, the arrangement shown is similar to that from FIG.4, with the result that the second small paint pipes 52 are in turnarranged midway between a fifth sound face 66 and a sixth sound face 68.As a difference from the sound faces shown in FIG. 4, the fifth soundface 66 and the sixth sound face 68 are made up of planar subfaces, theform of which however resembles a portion of the generated surface of acylindrical body. In this way too, widening of the region of the maximumsound particle velocity in the standing ultrasonic field is likewiseachieved.

Finally, FIG. 6 shows a sixth ultrasonic standing-wave atomizerarrangement, which is based on the arrangement of the first sonotrode 12with the first reflection body 14, as shown in FIG. 1. The referencenumerals have been correspondingly taken over from FIG. 1. In this case,three second small paint pipes 72 are arranged in a way corresponding tothe pieces of pipe 30, 31, 32, as shown in FIG. 1, and therefore have anequal distance from the sonotrode 12 and from the first reflection body14, which is shown here by indicating the second distance 36. Also shownin this figure are three third small paint pipes 74, which are shown inthe position which corresponds to the position of the pieces of pipe 30,31, 32 in FIG. 2. That is to say that the distance between the thirdsmall paint pipes 74 and the sound body 18 corresponds to the thirddistance 38 according to FIG. 2. This is correspondingly drawn in thisfigure. In this refinement of the subject-matter of the invention, it istherefore provided that a total of six small paint pipes 72, 74 arearranged between the first sonotrode 12 and the first reflection body14, to be precise respectively in two groups of in each case three smallpaint pipes 72, 74, with the result that three small paint pipes 74 arerespectively arranged at the second maximum of the sound particlevelocity, proceeding from the sound body 18, and three small paint pipes72 are arranged at the third maximum, and consequently over the maximumof sound particle velocity. With such an arrangement, the rate of thepaint atomization can be increased still further.

In none of the arrangements given above as examples was it shown indetail which further measures can act favourably on the atomization oron the painting process as such. For example, cleaning air can be usedin the generally known way for substantially avoiding adherence ofatomized paint to the sonotrode or to the reflection body. In addition,directing air can be used to make the atomized paint particlespreferably fly in the desired direction of painting. The process ofdirected painting can also be assisted by the paint particles beingelectrostatically charged. This charging may be achieved internally, inthe generally known way, that is to say with paint that is at ahigh-voltage potential being fed in, or by what is known as externalcharging, which usually charges the atomized paint through needles whichcarry a high voltage and are arranged in the vicinity of the atomizinglocation. The workpiece to be painted is then usually connected to earthpotential, so that the electrically charged paint particles preferablyfly towards the workpiece. A combination of internal and externalcharging is also quite possible.

Otherwise, it is quite conceivable that the reflection body is a furthersonotrode, with the particular advantage that the standing ultrasonicfield can be formed particularly strongly. Moreover, such a measureimproves the controllability of the ultrasonic field.

LIST OF DESCRIPTION

-   10 first ultrasonic standing-wave atomizer arrangement-   12 first sonotrode-   14 first reflection body-   16 basic body-   18 first sound body-   20 first sound face-   22 second sound face-   24 first line-   26 second line-   28 centre axis-   30 first piece of pipe-   31 second piece of pipe-   32 third piece of pipe-   34 first distance-   36 second distance-   38 third distance-   39 fourth distance-   40 second ultrasonic standing-wave atomizer arrangement-   42 fourth piece of pipe-   43 fifth piece of pipe-   44 sixth piece of pipe-   46 second reflection body-   48 second sonotrode-   50 third ultrasonic standing-wave atomizer arrangement-   52 first small paint pipes-   54 second sound body-   56 third sound body-   58 fourth sound body-   60 fourth ultrasonic standing-wave atomizer arrangement.-   62 line-   64 projections-   66 fifth sound face-   68 sixth sound face-   70 fifth ultrasonic standing-wave atomizer arrangement-   72 second small paint pipes-   74 third small paint pipes-   80 sixth ultrasonic standing-wave atomizer arrangement

1. Ultrasonic standing-wave atomizer arrangement for producing a paintspray mist for painting a workpiece, with a sonotrode, with a componentarranged lying opposite the sonotrode, a standing ultrasonic field beingformed in the intermediate space between the sonotrode and the componentin the case of operation, and with a paint-feeding device, by means ofwhich paint can be fed into the vicinity of a maximum of the soundparticle velocity of the ultrasonic field, wherein the paint-feedingdevice has in the region of the standing ultrasonic field at least twopieces of pipe for discharging paint, and in that at least two of thepieces of pipe are arranged in the region of a selected maximum of thesound particle velocity of the standing ultrasonic field.
 2. Ultrasonicstanding-wave atomizer arrangement according to claim 1, wherein thecomponent is a further sonotrode.
 3. Ultrasonic standing-wave atomizerarrangement according to claim 1, wherein the distance between thepieces of pipe in the region of the selected maximum is so great thatsheets of paint that are separate from one another are formed for eachpiece of pipe.
 4. Ultrasonic standing-wave atomizer arrangementaccording to claim 1, wherein the paint outlet openings of the at leasttwo pieces of pipe in the region of the selected maximum of the soundparticle velocity of a standing ultrasonic wave are arranged on animaginary straight line, and in that the straight line is perpendicularto an imaginary centre line which passes through the centroids of theopposing sound faces of the sonotrode and of the component. 5.Ultrasonic standing-wave atomizer arrangement according to claim 4,wherein the shape of the sound faces corresponds approximately to asegment of the generated surface of a cylinder reproduced withpolyhedral surfaces, or the segment is cylindrical, and in that thelongitudinal axis of the cylinder concerned is situated parallel to thestraight line.
 6. Ultrasonic standing-wave atomizer arrangementaccording to claim 1, wherein three of the pieces of pipe are arrangedin the region of a selected maximum of the sound particle velocity of astanding ultrasonic wave, and in that these pieces of pipe or theirpaint outlet openings are arranged in a triangle, in particular anequilateral triangle.
 7. Ultrasonic standing-wave atomizer arrangementaccording to claim 6, wherein the surface which is determined by thetriangle is perpendicular to an imaginary centre line which passesthrough the centroids of the opposing sound faces of the sonotrode andof the component.
 8. Ultrasonic standing-wave atomizer arrangementaccording to claim 1, wherein the distance between the at least twopieces of pipe arranged in the region of a selected maximum of the soundparticle velocity of a standing ultrasonic wave and the sonotrode is atmost equal to the distance between these pieces of pipe and thecomponent.
 9. Ultrasonic standing-wave atomizer arrangement according toclaim 1, wherein the at least two pieces of pipe are provided with ahydrophobic surface, in particular a tetrafluoroethylene coating. 10.Ultrasonic standing-wave atomizer arrangement according to claim 1,wherein there is a flow of cleaning air, by which wetting of thesonotrode and/or of the component is avoided or reduced.
 11. Ultrasonicstanding-wave atomizer arrangement according to claim 1, wherein thereis a flow of directing air, by which the direction of flight of thepaint spray mist can be influenced.
 12. Ultrasonic standing-waveatomizer arrangement according to claim 1, wherein there is at least onecharging device for internal and/or external charging, by which thepaint or the atomized paint particles can be electrostatically charged.